VGO is a hydrocarbon fraction that may be converted into higher value hydrocarbon fractions such as diesel fuel, jet fuel, naphtha, gasoline, and other lower boiling fractions in refining processes such as hydrocracking and fluid catalytic cracking (FCC). However, VGO feed streams having higher amounts of nitrogen are more difficult to convert. For example, the degree of conversion, product yields, catalyst deactivation, and/or ability to meet product quality specifications may be adversely affected by the nitrogen content of the feed stream. It is known to reduce the nitrogen content of VGO by catalytic hydrogenation reactions such as in a hydrotreating process unit. The current economic conditions and oil reserve situation worldwide have resulted in a growing interest in processing heavy oils and even extra-heavy oils with a much higher nitrogen content. There has been an increase in the nitrogen content of feeds to hydrocrackers in recent years. Removal of nitrogen is essential to prevent catalyst poisoning in downstream refinery processes such as hydrocracking (HC), catalytic cracking, and reforming. Organic nitrogen can be removed catalytically by hydrodenitrogenation (HDN), which is one of the most difficult hydrotreatment reactions.
Most of the difficult to remove nitrogen is present as heterocycles with multiple aromatic rings. The N-containing compounds are usually divided into two classes, basic and neutral compounds. Basic nitrogen compounds are primarily 6-membered-ring nitrogen compounds, such as quinolines and benzoquinolines. Nonbasic compounds are primarily 5-membered-ring compounds, such as indoles and carbazoles. Half of the total nitrogen is typically concentrated in the heaviest 30% of heavy feeds, with carbazole compounds substituted at position 1 being the most abundant. Di and trimethylcarbazoles with substitution at position 1 have been observed to be the most predominant. The problem of nitrogen compound inhibition has received considerable attention because the effects influence both process and catalyst development. Organic nitrogen compounds have a significantly negative kinetic effect on hydrotreating reactions such as hydrodesulfurization (HDS), on other hydrogenolysis reactions, and on hydrogenation reactions. The poisoning of the more acidic catalysts employed in hydrocracking caused by nitrogen compounds is even more severe, and the detrimental effect is reflected in the performance of the hydrocrackers. In particular, refractory nitrogen compounds with aromatic rings are resistant to reaction during hydrotreating processes that are currently used.
Hydroprocessing includes processes which convert hydrocarbons in the presence of hydroprocessing catalyst and hydrogen to more valuable products.
Hydrocracking is a hydroprocessing process in which hydrocarbons crack in the presence of hydrogen and hydrocracking catalyst to lower molecular weight hydrocarbons. Depending on the desired output, a hydrocracking unit may contain one or more beds of the same or different catalyst. Slurry hydrocracking is a slurried catalytic process used to crack residue feeds to gas oils and fuels. Hydrotreating is a hydroprocessing process used to remove heteroatoms such as sulfur and nitrogen from hydrocarbon streams to meet fuel specifications and to saturate olefinic compounds. Hydrotreating can be performed at high or low pressures, but is typically operated at lower pressure than hydrocracking.
Various processes using ionic liquids to remove sulfur and nitrogen compounds from hydrocarbon fractions are known. U.S. Pat. No. 7,001,504 B2 discloses a process for the removal of organosulfur compounds from hydrocarbon materials which includes contacting an ionic liquid with a hydrocarbon material to extract sulfur containing compounds into the ionic liquid. U.S. Pat. No. 7,553,406 B2 discloses a process for removing polarizable impurities from hydrocarbons and mixtures of hydrocarbons using ionic liquids as an extraction medium. U.S. Pat. No. 7,553,406 B2 also discloses that different ionic liquids show different extractive properties for different polarizable compounds. However, these processes do not show utility in removing refractory nitrogen compounds.
There remains a need for improved processes that enable the removal of compounds comprising refractory nitrogen from vacuum gas oil (VGO) either before or after hydrotreating. These refractory nitrogen compounds are difficult to remove by hydrotreating or hydroprocessing.